Electrical fluid heating device

ABSTRACT

An electric heating device for heating flowing fluid includes a tubular body of electrical insulation material adapted for through flow of the media. A plurality of porous electric heating elements of disc-like form electrically connected in series span the tube at intervals and are arranged in series in the direction of flow. Each heating element is pervious to fluid flow and is comprised of electrically conductive fibers or whiskers felted together. The heating elements are interspersed with non-heating homogenizing zones located between adjacent heating zones. In one embodiment each homogenizing zone merely comprises an empty space. In another embodiment the homogenizing zones comprises a porous mass of electrically conductive fiber skeletons. The pore volume and electrical conductivity of the homogenizing mass are very much greater than those of the porous heating elements and the homogenizing masses form the electrical connections whereby the heating elements are connected electrically in series.

[111 3,826,895 July 30, 1974 ELECTRICAL FLUID HEATING DEVICE [75] Inventor: Hermann J. Schladitz, Munich,

Germany Assignee: Schladitz-Whiskers A.G., Zug,

Switzerland Filed: May 8, 1973 Appl. No.: 358,344

[30] Foreign Application Priority Data May 10, 1972 US. Cl 219/382, 219/307, 219/338, 219/374, 338/54,-338/205 Int. Cl 1105b 3/10, F24h 1/10 Field of Search 219/307, 319, 338, 374, 219/381, 382, 375, 376; 338/204, 205, 223225, 54

1.096.375 12/1967 Great Britain ..2l9/38l 487,436 4/1918 France ..2l9/38l ELECTRICALLY CONDUCTIVE NON-HEATING HOMOGENIZING ZONES Germany 2222849 512,845 10/1920 France 219/381 Primary Examiner-A. Bartis Attorney, Agent, or Firm-Kane, Dalsimer, Kane, Sullivan and Kurucz [5 7 ABSTRACT An electric heating device for heating flowing fluid includes a tubular body of electrical insulation material adapted for through flow of the media. A plurality of porous electric heating elements of disc-like form electrically connected in series span the tube at intervals and are arranged in series in the direction of flow. Each heating element is pervious to fluid flow and is comprised of electrically conductive fibers or whiskers felted together. The heating elements are interspersed with non-heating homogenizing zones located between adjacent heating zones. In one embodiment each homogenizing zone merely comprises an empty space. In another embodiment the homogenizing zones comprises a porous mass of electrically conductive fiber skeletons. The pore volume and electrical conductivity of the homogenizing mass are very much greater than those of the porous heating elements and the homogenizing masses form the electrical connections whereby the heating elements are connected electrically in series.

3 Claims, 2 Drawing Figures ELECTRIC HEATING ELEMENTS PAIENTEDJMOW V 3.826.895

F/GJ F/6.2

,5 %%B%'#v' g ELECTRIC HEATING ELECTRIC NON-HEATING M N S HEATING HOMOGENIZING ELEMENTS 6 ZONES 6 HOMOGENIZING ZONES ELECTRICAL FLUID HEATING DEVICE BACKGROUND OF THE INVENTION This invention relates to electrical heating devices. It is particularly concerned with the rapid heating of fluid media such as gases, liquids, vapors or aerosols.

A well known heating device, described in German Pat. No. 1,288,705 has a heating element consisting of a plurality of electrically conducting filaments felted and in metallic contact with one another. These filaments are preferably so-called whiskers, and through the felt flows the medium to be heated. Such a heating element offers to the fluid medium to be heated a very large heating surface, and at the same time it displays a very low resistance to flow, so that the medium can be heated to a determined temperature in an extremely short time.

In order to arrive at the desired final temperature, the medium among other things must be in contact with the heating element for a certain length of time which is related to the length of the heating element in the direction of flow and to the rate of flow. High rates of flow require a longer heating element to attain a determined final temperature than is necessary than with low rates of flow. A long heating element consisting of an electrically conducting fiber skeleton cannot, however, in practice be made with the necessary homogeneity, so that it is unavoidable that certain points of the fiber skeleton are more densely felted than others. During the heating of a fluid, these dense points are heated more strongly than the others owing to the greater resistance to fluid flow and the greater electrical current flow. If the fluid is a liquid this can cause local evaporation while the temperature of the liquid elsewhere remains well below the evaporation point. The vapor bubbles interfere with the flow of liquid through the heating element to a considerable extent. This can be related to the fact that the volume passed through a capillary suddenly drops when the liquid has reached its boiling point.

Moreover, if a long and inevitably non-homogeneous heating element is to be used for heating mixtures of hydrocarbons such as petrol, diesel oil or fuel oil, there exists in the region of the dense points the risk that the readily volatile constituents will evaporate while the less easily volatilized hydrocarbons will remain behind and gradually crack. A blockage may then occur, which will bring about increased electrical conductivity. The tendency will be for the electric current to concentrate its flow through these points of increased conductivity to the detriment of the other parts of the fiber skeleton which will no longer be adequately heated.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved electrical heating element, still using felted electrically conductive fibers or whiskers.

According to the present invention there is provided an electrical heating device for heating fluid media comprising a body adapted for through flow of said media and electrical heating elements housed in said body and arranged in series in the direction of flow of said media, each element consisting of a plurality of electrically conducting fibers or whiskers felted together and in metallic contact with one another, and the heating elements being interspersed with homogenizing zones in which no appreciable heating of the media takes place.

Thus the heating device is divided into individual, consecutive heating stages. Each element can be made substantially homogeneous with uniform porosity of the fiber skeleton. This is because they can be relatively short, for example with lengths of l to 5 mm. Even if there is a lack of homogeneity in the fiber skeleton, leading to excessive heating of the fluid medium, there takes place in the intermediate stages, or homogenizing zones, a mixing of the hotter and cooler constituents so that, on entering the next heating element, the fluid again displays a homogeneous temperature. The intermediate stages therefore prevent the paths of vapor bubbles derived from the dense points of the heating elements extending throughout the heating device. In the case of heating mixtures of hydrocarbons, short circuit bridges that may have been produced through cracking at the dense points can be propagated at most as far as the nearest intermediate stage. Therefore the risk of a considerable reduction in the electrical resistance of the whole heating device and therefore a fall in the heating performance need not be feared.

The intermediate stages or homogenizing zones can be formed by empty spaces, in which any vapor bubbles formed can dissolve in the liquid. Alternatively they may be formed by electrically conducting fiber skeletons whose pore volume and electrical conductivity are considerably greater than those of the heating stages. In each such fiber skeleton, which owing to its greater conductivity participates only slightly in the heating of the fluid medium, intensive mixing of the vapor and liquid components can be achieved.

The neighboring heating elements are for preference separated from one another by distance pieces which also establish the electrical connection between the heating stages. These distance pieces can be formed from tubular bodies, each of which surrounds an empty space representing an intermediate stage. Alternatively, the distance pieces can be formed by the aforementioned electrically conducting fiber skeletons whose fibers or whiskers have a cross-section which may be a multiple of the cross-section of the whiskers forming the heating elements.

Preferably, the electrical heating device body is tubular and of electrically insulating material, the heating elements being of disc-like form spanning the tube at intervals. If directly heated by an electric current, the supply is conveniently to contacts on the first and last heating elements. It is also possible, however, for these to be arranged within an induction coil.

The fibers forming the heating elements are for preference polycrystalline metal whiskers with a diameter of, for instance, 0.5 to 20 pm, as such whiskers are distinguished for extremely high strength and thus can withstand high fluid pressures without breaking and being carried along by the liquid. However, other filaments can successfully be used, for instance metallized carbon filaments. Al O whiskers or filaments, or quartz filaments.

The metallic connection of the fibers at their points of contact can be effected by any of a number of well known methods for instance by metallizing in the gas phase, welding by brief local melting with the aid of coherently bunched light rays, electron beam welding, ultrasonic welding, the galvanic separation of metals or by currentless metal coating.

By the term polycrystalline metal whiskers is meant extremely fine metal filaments or hairs which have grown from the gas phase, such as are described in German Pat. No. 1,224,934. The ratio between the diameter and length of these whiskers, or of the other previously mentioned fibers, can amount to more than 111000.

The inventionimay be performed in various ways and some constructional forms thereof will now be described, by way of example, with reference to the ac companying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a longitudinal section through a first form of electrical heating device according to the invention; and

FIG. 2 is a longitudinal section through a second form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The heating device of FIG. 1 has a tubular jacket 1 of electrically insulating material in which are fitted several disc-like heating elements 2 arranged and connected in series with respect to the direction of flow S of the fluid medium to be heated. Each heating element 2 consists of a plurality of electrically conducting filaments, preferably so-called whiskers, which are felted together and connected metallically with one another at their contact points. Neighboring heating elements 2 are separated from one another by distance pieces 3, which also serve to establish the electrical connection between the heating elements. These distance pieces 3 are each formed by a tubular body fitting closely within the tubular jacket 1 and each bounding an empty space 4 representing an intermediate stage. In order to increase the mechanical strength and to obtain a homogeneous flow, wire lattices or filters are arranged between the distance pieces 3 and the neighboring heating elements 2 and cover the circular faces of the elements 2. The first and the last heating elements 2 are provided with respective contact plates 6 in the form of sieves or filters, which are connected to the positive and negative poles of a source of current. As the fluid medium passes through the heating device it is heated step by step by the consecutive heating elements 2 to higher and higher temperatures, until on leaving the final heating element 2 it has reached the final temperature desired. In the intermediate stages formed by the cavities 4, which can also be described as mixing or homogenizing zones, there occurs the temperature homogenizing of the medium heated in the previous heating elements, so that on entering the following heating element, the medium has a substantially uniform temperature, and any vapor bubbles formed in the heating of liquids are dissolved. The disc-like heating elements 2 can be made by machine with largely uniform pore size, without great difficulty and expense. The number of heating elements connected in series is optional and depends on the final temperature desired, on the rate 4 of flow and on the electrical power available.

The heating device of FIG. 2 differs from that of FIG. 1 mainly in that the intermediate stages between neighboring heating elements 2 are not formed by empty spaces, but by filament skeletons 7, which have in principle the same structure as those of the heating elements 2, but possess a larger pore volume and very much greater electrical conductivity. These skeletons 7 further the mixing of the components of the medium that are already in the form of vapor with those that are still liquid.

In a practical example of such a heating device the heating elements 2 consist of polycrystalline iron whiskers with an average diameter of about 1 pm and the skeleton has a pore volume of about 65 percent and an electrical resistance of about 1 ohm. The filament skeletonof each intermediate stage 7 may consist of whiskers with a diameter of about 40 pm and a a pore volume of about percent and an electrical resistance of about 0.01 ohm.

Thus several aforenoted objects and advantages are most effectively attained. Although a single, somewhat 1. An electrical heating device for heating fluid.

media comprising a body having a first end and a second end and adapted for through flow of said media and a column of electrical heating elements having a first and second end and housed in said body between the body ends, the heating elements being arranged normal to the direction of fluid flow and in series in the direction of flow of said media to form adjacent heating zones, each element being pervious to fluid flow and comprised of a plurality of electrically conducting fibers felted together, the heating elements being interspersed with homogenizing zones in which no appreciable heating of the media takes place, each homogenizing zone being between adjacent heating zones, each of said homogenizing zones comprising a porous mass of electrically conducting fiber skeletons pervious to fluid flow whose pore volume and electrical conductivity are very much greater than those of the heating elements, the homogenizing skeletons forming electrical connection between adjacent heating zones, whereby all heating zones are connected in series, and coupling means for coupling the column ends to an electric power source.

2. An electrical heating device as claimed in claim 1, wherein each said fiber skeleton consists of metal fibers whose cross-section is a multiple of the cross-section of the fibers forming the heating elements.

3. An electrical heating device as claimed in claim 1, wherein said body is tubular and of electrically insulating material, the heating elements being of disc-like form spanning the tube at intervals. 

1. An electrical heating device for heating fluid media comprising a body having a first end and a second end and adapted for through flow of said media and a column of electrical heating elements having a first and second end and housed in said body between the body ends, the heating elements being arranged normal to the direction of fluid flow and in series in the direction of flow of said media to form adjacent heating zones, each element being pervious to fluid flow and comprised of a plurality of electrically conducting fibers felted together, the heating elements being interspersed with homogenizing zones in which no appreciable heating of the media takes place, each homogenizing zone being between adjacent heating zones, each of said homogenizing zones comprising a porous mass of electrically conducting fiber skeletons pervious to fluid flow whose pore volume and electrical conductivity are very much greater than those of the heating elements, the homogenizing skeletons forming electrical connection between adjacent heating zones, whereby all heating zones are connected in series, and coupling means for coupling the column ends to an electric power source.
 2. An electrical heating device as claimed in claim 1, wherein each said fiber skeleton consists of metal fibers whose cross-section is a multiple of the cross-section of the fibers forming the heating elements.
 3. An electrical heating device as claimed in claim 1, wherein said body is tubular and of electrically insulating material, the heating elements being of disc-like form spanning the tube at intervals. 